The 2N3906 is a popular general-purpose PNP bipolar junction transistor (BJT) designed for low-power switching and signal amplification. Supplied in a compact TO-92 through-hole package, it is commonly used in switching circuits, signal amplifiers, LED drivers, high-side control circuits, oscillators, and general electronic projects.

The 2N3906 is the PNP complement commonly paired with the 2N3904 NPN transistor and is suitable for circuits requiring a small-signal PNP device.

Pin Configuration

For commonly available TO-92 versions, the pin configuration is typically:

Pin 1 – Emitter
Pin 2 – Base
Pin 3 – Collector

Pin arrangement can vary between manufacturers, so always verify the datasheet for the exact component supplied before PCB assembly.

Technical Specifications

• Transistor Type: PNP Bipolar Junction Transistor (BJT)
• Package: TO-92
• Collector-Emitter Voltage (VCEO): -40V Max.
• Collector-Base Voltage (VCBO): -40V Max.
• Emitter-Base Voltage (VEBO): -5V Max.
• Continuous Collector Current (IC): -200mA Max.
• DC Current Gain (hFE): Device- and operating-condition dependent; commonly specified across a range up to approximately 300
• Mounting Type: Through-Hole
• Typical Use: Switching and Signal Amplification

How the 2N3906 Works

As a PNP transistor, the 2N3906 turns on when its base voltage is sufficiently lower than its emitter voltage.

For a silicon transistor, the forward base-emitter voltage is typically around 0.6-0.7V when conducting. The 5V specification found in some descriptions refers to the maximum emitter-base reverse voltage (VEBO) and should not be confused with the normal operating base-emitter voltage.

When used as a switch, the transistor is generally operated between the cut-off and saturation regions.

Using the 2N3906 as a Switch

The 2N3906 is commonly used for high-side switching in low-current circuits.

In a typical PNP switching arrangement, the emitter is connected toward the positive supply. Pulling the base sufficiently below the emitter voltage turns the transistor on, while bringing the base close to the emitter voltage turns it off.

A suitable base resistor should be used to limit base current.

The base resistor can be estimated from the voltage across the resistor and the required base current:

RB = (VDRIVE − VBASE) / IB

The exact calculation depends on the circuit configuration and supply voltage.

Using the 2N3906 as an Amplifier

The 2N3906 can also be used as a small-signal amplifier when operated in its active region. Contrary to the original description, a maximum gain figure of around 300 does not make it unsuitable for amplification.

Typical amplifier configurations include common-emitter, common-collector, and common-base circuits.

DC current gain is expressed as:

hFE = IC / IB

Actual gain varies with collector current, temperature, operating voltage, and individual transistor characteristics.

Complementary Pair with 2N3904

The 2N3906 PNP and 2N3904 NPN are commonly used together as complementary transistors.

This combination can be useful in:

• Push-pull circuits
• Signal switching
• Complementary driver stages
• LED control
• Small amplifier stages
• Logic interfacing
• General electronic circuits

Applications

The 2N3906 is commonly used in low-current switching circuits, high-side switches, LED drivers, signal amplifiers, oscillators, inverter circuits, converter control circuits, complementary transistor stages, siren circuits, LED flashers, sensor interfaces, and general-purpose electronics.

It can also be used with other transistors in suitable Darlington or complementary configurations.

Important Notes

The 200mA collector current is an absolute maximum rating, not a recommended continuous operating current for every circuit. Safe operating current depends on collector-emitter voltage, power dissipation, ambient temperature, PCB design, and the manufacturer's specifications.

The 5V rating refers to the maximum emitter-base reverse voltage (VEBO). It does not mean that the transistor requires 5V between base and emitter to turn on.

The base current is also not 200mA. Base current must be appropriately limited according to the circuit requirements and transistor ratings.

When switching inductive loads such as relays, solenoids, or small motors, appropriate transient protection such as a flyback diode should be used.

Always verify the pinout and electrical ratings against the datasheet for the exact manufacturer supplied.

Package Includes

1 × 2N3906 PNP Transistor